Purpose:
To objectively evaluate the effectiveness of two ocular surface lubricants in subjects with dry eyes, by studying the changes in ocular surface temperature (OST) and compare the results to a saline eye drop (control) in a double masked study.

Methods:
15 eyes of subjects clinically diagnosed with dry eye were randomized to receive two tear drops, drop A (propylene glycol and glycerin containing drop) and drop B (carbomer containing drop) and the OST changes were compared to that of a control saline drop (Ocufresh eye wash), on three separate days.The OST was measured using a non-invasive infrared thermal camera (Thermovision SC325, FLIR System, sensitivity <0.05°C at +30°C, 30HZ frame rate, 320X240 resolution, accuracy ± 2% with emissivity set at 0.98) at baseline (before drop), 5 min, 15 min and 30 min after drops.Thermal data was analyzed using custom software to calculate the initial OST, average OST and slope of OST in the central 9 mm of the cornea over a five second blink interval. Statistical analyses were performed using t-tests.

Results:
No significant changes in initial OST were observed with any of the drops. With drop A, there was an increase in average OST from 5 min (34.14 ±0.15°C) to 15 min (34.46 ±0.11°C, p=0.006) , and a decrease in OST from 15 min to 30 min (34.29 ±0.11°C, p=0.02) after drop instillation. With drop B, there was a decrease in the OST from baseline (34.17 ±0.13°C) to 5 min (33.8 ±0.16°C, p=0.04), returning to baseline at 15 min (34.05 ± 0.17°C, NS). With saline, no significant change in average OST was observed.On comparing the study drops to saline, change in OST from baseline with drop A was greater at 5 min (-0.11°C, NS), 15 min (0.12°C, p=0.02) and 30 min(-0.13°C, p=0.01). No significant change in OST was noticed between drops B and saline. With drop A, the rate of OST cooling was lower at 15 min (-0.06°C/sec, p=0.03) and 30 min (-0.07°C/sec, p=0.04) than at 5 min (-0.09°C/sec, NS), when compared to baseline (-0.1°C/sec). No significant changes in the OST cooling rate was noticed with drops B and saline.

Conclusions:
A combination of Propylene glycol and glycerin containing eye drop helps increase the OST in dry eyes better than a carbomer containing drop. This may indicate decreased evaporation with drop A. Thermal imaging helps study the effectiveness of ocular surface lubricants and has the potential for usage in the study of different dry eye treatments.